Although the present invention is not directed to specialized leather processing techniques for obtaining esoteric leather finishes, the present compositions in no way hinder obtaining these effects. A more detailed discussion of specialized processing together with conventional processing procedures can be found in Kirk Othmer's Encyclopedia of Chemical Technology, Volume 10, pages 295-309 and Volume 12, pages 303-341 as well as Modern Practice in Leather Manufacture by J. A. Wilson, 1941, Reinhold Publishing Corp., pages 170-516 and 556-700. The present invention is directed to wet processing treatments of natural and synthetic hides, skins and furs and to the improved penetrating, softening, lubricating and water resistant properties imparted by the present formulations when incorporated in the respective baths employed in leather manufacture. More particularly, the invention is directed to a novel processing aid for hastening and improving soaking, deliming, tanning, fat-liquoring, base coating and finishing of natural or synthetic hides and pelts.
The production of finished leather has many variations depending upon the desired end product and characteristics of the hides but, in general, involves the following basic processing treatments.
Animal hides generally contain about 1% ash, 65-70% water and 30-35% dry substances which include fibrous proteins such as keratin, elastin, reticulin and the leather making protein, collagen, which is responsible for the strength and toughness of the raw hide and whose structural changes are important to ageing. The tanning process consists of a number of collagen-purification steps prior to the actual tanning of the hide. If most of the minor proteins of the hide are not removed before the tanning, they prevent the resulting leather from being soft and flexible.
When a hide is removed from the carcass, the first concern is to preserve or cure that hide so that it is protected until it can be transported to a tannery for manufacture into leather. Curing has been effected by salting the hides in a solid pack in which the hides were laid out flat and covered with a minimum of 1 kg salt/kg hide. The salt dissolved in the water in the hide, forms brine, and dehydrates the hide, thereby inhibiting autolysis and growth of bacteria. After the hides are drained for 30 or more days, they are sorted and bundled for delivery to the various tanners. More modern techniques of curing involve soaking in a saturated salt solution in a raceway that holds several hundred hides which are continually tumbled in a salt solution held at the saturation level. Such treatment removes water from the hide to prevent microbial growth. A bactericide is generally added to assist in preserving the hides. Full salt penetration and dehydration by this more modern method still requires from 18 to 24 hours. Accordingly, there is a need to reduce the curing time in commercial operations. In addition, the cured hides are usually fleshed to remove fatty tissue adhering to their undersides before shipment to tanners. In general pretanning treatments include subjecting a pelt to a 20-35 hour cure by a wet process involving immersion in a solution of brine containing bactericide or by a dry green-salt process, such as stacking hides which are layered with dry salt, for a period of 2 to 5 weeks at below room temperature.
Frequently, a pre-wash for the removal of flesh tissue prior to curing is employed. The cured dehydrated hides are then soaked in water for 3 to 30 hours after which beaming is completed. The beamed material is again water washed in the presence of a softening agent, e.g. between about 0.1 and about 0.5% sodium sulfide, soda ash, or sodium tetrasulfide, to effect rehydration. Disinfectants may also be added at this stage to offset bacterial degradation.
The final removal of epidermis and hair is carried out in a series of vats at a temperature ranging from about 50.degree. to about 85.degree. F. by contacting the hide with 10-15% by weight of aqueous saturated lime solution for a period of several days. The liming solution contains calcium oxide, calcium hydroxide and may also include an accelerator or sharpening agent, such as sodium sulfide, sulfhydrate, cyanide salts or dimethylamine, at a concentration of from 2 to 5% by weight of hide. Since the combined effluents from this deliming stage contain between 16 and 18% solids, a serious waste disposal problem exists which is equalled only by the disposal of effluents from bating, soaking, tanning, coloring and fat-liquoring.
The limed hides are then neutralized and bated with buffering agents such as ammonium sulfate or chloride and a proteolytic enzyme, such as trypsin or Oropon, at elevated temperature for the removal and alteration of certain proteins and for reducing the swelling of protein constituents in the skin. The delimed and bated skins are then rinsed with water and are ready for tanning.
Tanning processes are varied and complex but primarily include vegetable tanning for heavy leathers, chrome tanning for lighter hides and skins, or tanning with sulfonated oils, Syntans, or zirconium, alum or iron salts or urea- and/or phenol-formaldehyde resins. A serious problem in the leather industry exists in metal tanning since as much as 25-30% of the metallic agent does not exhaust from the tanning bath into the hide fibers. As a result, a large amount of tannage is lost in draining drums after the initial tanning which results, not only in inefficient use of materials, but also in a serious effluent disposal problem contributing to the pollution of rivers and waterways. Accordingly, an aim of the present invention is to provide for substantially complete exhaustion of the metal onto the leather fibers and, by efficient use of the metal tannage, to reduce the quantity of metal salts required for effective tanning of leather and overall tanning time.
After the initial tanning is completed, the hides may be retanned by one or more of the above processes or they may be passed directly to the finishing stages of processing which include fat-liquoring, at least partial drying, and optionally bleaching, drying and scouring, with, for example, sodium carbonate, sodium hydroxide, hydrated sulfuric acid, sodium bisulfite, sulfurous acid, sulfite cellulose solutions or Syntans. Fat-liquoring with mineral and vegetable oils, soaps or sulfated oil emulsions at 110.degree.-140.degree. F. to lubricate the leather fibers generally follows tanning. The leather may be additionally processed by oiling with sulfated oils or soaps in the presence of an alkaline salt, stuffing with fish oil, mineral oils, oxidized fish oil greases, carnauba, paraffin and other waxes or combinations of these at a higher temperature, e.g. 150.degree.-225.degree. F. to impart water repellency and finally dyeing with acid, base or direct dyes, pigments or lakes and/or spraying with shellac, albumin, lacquer or resins and then mechanically treating to provide gloss, embossing, or napping for desired texture.
It will be appreciated that the above processing steps minimally require several weeks and often require several months of treatment in order to produce a fully processed hide. Accordingly, it is an object of the present invention to reduce the number of finishing steps and to shorten the time required for effecting certain process treatments while providing hides and pelts, including fur pelts, of higher tanning penetration, greater flexibility, moisture-content and resistance to cracking or ageing.
According to this invention, a N-heterocyclic lactam containing from 10 to 24 carbon atoms is employed to replace or augment certain processing solutions in the wet treatment of leather.
The present lactams are those having a 5 to 7 membered ring which are represented by the formula ##STR1## and isomeric forms thereof, wherein n has a value of from 1 to 3 and R is a saturated or unsaturated hydrocarbon radical of 6 to 18 carbon atoms which includes alkyl, alkenyl and alkinyl radicals such as for example, octyl, decyl, dodecyl, tetradecyl, cetyl, heptadecyl, octadecyl, octenyl, decenyl, dodecenyl, hexadecenyl, decinyl, tetradeciny radicals and conjugated and non-conjugated unsaturated hydrocarbon radicals of oils and fats as represented by caprylic, oleic, palmitic, palmitolic, parinaric, undecylic, isanic, myristic, ricinoleic, linoic, linolenic, lauric and stearic acids as well as mixtures of these as found in naturally occurring fats and oils such as tallow oil, cocoa oil, palm oil, animals fats, rapeseed oil, corn oil, linseed oil, tung oil, isano oil, sardine oil, castor beans, and the like. Of these, the N-alkyl and N-olefinically substituted-2-pyrrolidones are preferred and the N-alkyl-, N-tallow- and N-coco-substituted types are most preferred.
The lactams of this invention can be directly incorporated into an existing formulation used in beaming tanning or finishing or an aqueous solution of the lactam may be added to such formulations for better control of concentration when small amounts are required. Also, aqueous solutions of the lactams may be used individually or in combination as the sole active agent to achieve desired results and specific effects.
It is noted that lactams having N-alkyl substitution of C.sub.8 to C.sub.14 preform primarily as surfactants; whereas the primary property of C.sub.16 +N-alkyl lactams is their complexability with other organic and inorganic compounds. However, all of the present lactams possess some degree of surface activity and complexing properties.
As an additive, between about 0.01 and about 10 weight % of the present amides can be incorporated in beaming and/or tanning solutions to impart increased and accelerated penetration of active agents while preserving the softness and flexibility of the hide. As a replacement for an auxiliary treating agent, used primarily in the finishing stages of leather processing to soften, moisturize, fill and/or form an adhesive base coat, and in the pretanning stages, to hasten hide rehydration and loosening of hair or epidermis or to neutralize residual time and provide improved accessibility of the skin for absorption of tannage, between about 0.5 and about 20% of the amide per weight of hide can be employed, as a solution, emulsion, dispersion or suspension in water, mineral or vegetable oils, polyoxyalkylene surfactants, lanolin, sulfonated oils, stearic acid, glycerin, glycols, or petroleum in water emulsions or suspensions.
Incorporation of the present lactams in metal tanning formulations provides for faster and more complete exhaustion of the metal onto the leather fibers so that a reduced amount of metal tannage can be applied to obtain the desired result. The tanning time of operations employing other tannages is also significantly reduced.
Generally, the amount of lactam required to achieve such reduction of processing time or exhaustion of tanning agent onto the hide is preferably between about 0.05 wt. % and 1 wt. %, most preferably between about 0.5 wt. % and about 5 wt. % based on tanning agent.
Utilization of the present amides in leather finishing treatment permits reduction in the number of coats normally required by combining the characteristics of a first or base coat, which provides good skin coverage and adhesion properties for bonding to the skin with the properties of subsequent coatings and finishing agents normally and separately employed for filling, softening, moisturizing and waterproofing. Since the present amides have good skin substantivity as well as moisturizing and viscosity building properties, they are multifunctional agents which accomplish in a single treatment that which has required several separate time consuming treatments to accomplish.
The present lactams are employed in the various treating stages at the temperature normally associated with said treatment under atmospheric pressure.
The present amide compositions provide excellent hide penetration, improved hide lubricity, good distribution of coloring agents and exhibit high tolerance for bactericides, and in some cases actually promote penetration of the bactericide into the epidermal and/or corium layers of the hide. Due to leather lubricating properties, they also possess good release properties in applications where leather embossing is required and have superior solubility or miscibility with water as compared to the oils and greases conventionally employed in leather finishes.
As briefly stated above, an important stage of treatment which can be benefited by addition of the present amides is metal tanning. Tribasic chromium sulfate or sodium dichromate based tannages are cationic and have strong affinity for the fiber protein of leather. However, the rapid exhaustion of chrome from the bath onto the fibers lacks the desired penetrative affect and often clogs the surface pores; thus, a surface protein reaction with consequent incomplete exhaustion of the chrome onto he fibers and inefficient use of the tannage results. Accordingly, processes have been developed to slow the rate of protein/chromium coordination formation to extend the interaction over a period of several days. However, when only 0.5 to 5 weight percent of the present non-ionic amide is added to the chrome salt bath mixture, tanning with deep hide penetration can be completed within 24 hours or less while retaining the degree of softness and hide pliability required for handling. Also the relatively complete exhaustion of metal, e.g. chrome from the treating solution into the leather, avoids serious waste disposal problems. Still further the efficient exhaustion of tanning agent allows for significant reduction in the amount of agent required for a desired degree of tanning. The same benefits are achieved upon addition of the present lactams to other metal tanning solutions, e.g. those employing zirconium, aluminum and ferric salts as well as vegetable tanning solutions.
The addition of lactam also mininizes or obviates the need for immediate addition of oils during tannage or the addition of oils, greases and waxes normaly applied to hide in subsequent stages.
Other benefits realized by the lactams of this invention include reduction in the number of finishing steps, thus providing a more simplified leather manufacturing process and shorter treatment time.
Examples of conventional vegetable tannages which may be combined with the present amides are those which yield catechols or pyrogallols upon distillation. Condensed tannins are of the phenol type; whereas others are esters of glucose or similar sugars with one or more trihydroxybenzoic acids. Generally the tanning agent is a complex blend of these glucosides and phenols. The individual components of the mixture are derived extracts from pods, roots, fruits and leaves, bark or wood of quebracho, wattle, eucalyptus, gambier, valonia, alder, birch, chestnut, spruce, oak, hickory, larch, angica, weeping willow, dhawa, mangrove, algarobilla, cascalote, hazel, tara, manna gum and sumac trees and pomegranate, myrobalam, hannoki and honeysuckle fruits and shrubs.
The original color of the above tannins varies from yellow to brown which is darkened on exposure to light and consequently darkens the hide during treatment. Accordingly, it is beneficial to use as little as possible to achieve a desired tanning effect. The present nonionic surfactant lactams, which are colorless compounds, provide more efficient use of these tanning agent by rapidly transporting them into the pores of the hide and, hence lesser amounts of the tannins are required. Basically, the tannins are astringents which are normally soluble in water, acetone and alcohol but which are insoluble in benzene, ether and chloroform. In acidic medium they transform leather protein into insoluble products which are resistant to decomposition. Specifically, the tannin mixtures of glucosides, various phenols and polyphenols combine with collagen fibers of the skin and liberate sugars. The protein of skins is capable of absorbing large quantities of tannin, to the extent that the weight of skin may be increased up to 350% its weight. However, as in the case of metal tanning, when absorption proceeds too rapidly, the surface pores become clogged so as to prevent further absorption of tannin, and even at lower tanning rates some clogging of surface pores usually occurs, thus causing the skin to become stiff and brittle. The non-ionic lactams of this invention possess the ability to complex with such compounds and transport these tannins into the epidermal and/or corium layer of the skin for more uniform and complete tanning at desirable rates of absorption while maintaining hide softness and pliability.
Syntans are often substituted for vegetable tannins in part or in all of the tanning process. Examples of syntans include condensation products of phenol-formaldehyde, melamine-urea and styrene-maleic anhydride. These may be augmented with a fraction of sulfite cellulose waste liquor, e.g. magnesium lignosulfonate. Since the present amides promote skin penetration, they are also beneficially employed with these tanning agents.
The C.sub.8 to C.sub.16 alkyl, N-tallowalkyl- and N-cocoalkyl-2-pyrrolidones of the present invention possess excellent percutaneous penetration and surfactant properties and thus increase the penetration of formulations containing tannages; fish, vegetable, mineral or animal oils, sulfated oils, oil greases and/or waxes and promote their adherence to the leather. For example, excellent penetration is achieved with the following aqueous formulations of the present lactams which provide examples suitable for incorporation in stuffing, tanning and fixing baths.
______________________________________ Stuffing Tanning Additive Chrome Salt Fixing ______________________________________ 5-10 wt. % 2-6 wt. % stearic acid 0.4-1.5 wt. % borax beeswax or NaHCO.sub.3 20-30 wt. % 0.5-3 wt. % isopropyl 12-15 wt. % amide* mineral oil myristate 0.5-3 wt. % glycerol monostearate 12-18 wt. % 0.5-2 wt. % triethanol amide* amine 1-10 wt. % sorbitol 1-5 wt. % amide* ______________________________________ *in the above examples the amide is N--octyl, N--decyl, N--dodecyl, N--cocoalkyl or N--tallowalkyl 2pyrrolidone or mixtures of these heterocyclic amides
The N-cocoalkyl-2-pyrrolidone is non-foaming, miscible with water up to about 40% and will form clear and stable aqueous cells above the miscibility level; whereas N-tallowalkyl-2-pyrrolidone is less water soluble but forms creamy gels with water in any proportion. These preferred amides, as well as the individual C.sub.8 to C.sub.16 alkyl lactams can be used with either hydrophilic or lipophilic emulsifiers or fatty acids and stearate based softening agents to enhance lubricity and hide softness.
Other amides falling within the scope of the present invention such as the N-substituted caprolactams and pyridinones are also effective in providing water and moisture barrier properties in the finishing stages of tanned leather. Further, the lactams of the present invention do not lump or agglomerate either in solutions or on the hides or pelts and are compatible with a wide variety of oils, fats, greases and waxes, as well as water and preform as emulsifiers, humectants and softening agents in natural or synthetic vegetable tannages as well as in metal salt and oil tannages.
Representative of compatible oils, fats and waxes are fish, vegetable, animal and mineral oils, sulfonated oils, esters of fatty acids, fatty acids, ethoxylated glyceryl monostearate, fatty alcohols, hydrogenated vegetable oils, fatty alcohol ethers, beeswax, polyethylene, polyhydric alcohols, glycerin, dimethicone, squalane, lanolin, paraffin, ceresin, acetylated lanolin, dimethyl- or methylphenyl-polysiloxanes, phospholipids, sterols, acetylated hydrogenated lard glyceride, corn oil, wheat germ oil, persic oil, petrolatum, neatfoot oil, castor oil, mink oil, sweet almond oil, and animal fats.
Formulations of the present amides beneficially include a hydrophilic and lipophilic emulsifier for converting oils, waxes and fats into solutions or emulsified form. Between about 0.5 and about 12% by weight of a C.sub.6 to C.sub.22 fatty acid, such as myristic, lauric, palmitic, oleic, linoleic, linolenic, stearic and erucic acids, or mixtures thereof, may be combined with between about 0.5 and about 8% by weight of a basic or neutral compound such as ammonia, imidazolidinyl urea, cetyl alcohol, triethanol amide, tripropanol amine, sorbitan, sorbitan sesquioleate, alkali metal salts of lactic, hydracrylic or hydroxybutyric acids, a polyoxylated vegetable oil (e.g. Emulphor.RTM.) an alkali metal borate, and the like. Combinations of these compounds as well as commercially marketed preparations, such as Polysorbate, Carbomer 934, 941, 940, etc., Choleth, i.e. Chloestrol, are among the emulsifiers suitably employed in the formulations of the present invention.
The present formulations may also contain between about 0.5 and about 10% by weight of a polyalcohol, or alkylated or alkoxylated alcohol humectant such as glycerine, sorbitol, mannitol, polyethylene glycol, polypropylene glycol, propylene glycol, butylene glycol, lanolin alcohol, polyoxyethylene glycol, polyoxypropylene glycol, glyceryl stearate, and the like.
Also, between about 0.5 and about 16% by weight of various softening agents such as a fatty acid ester of the types represented by sorbitan monostearate, glycerol monostearate, isopropyl myristate, gluconic acid, myristyl myristate, lauryl lactate etc., may be incorporated in the present amide formulations.
Having generally described the invention, reference is now had to the following examples which illustrate preferred embodiments, but which are not to be construed as limiting to the scope of the invention as more broadly described above and in the appended claims.